Of the plant materials grown for sale, transplanting, or experimentation by commercial landscape nurseries, the majority are now developed in containers on top of the ground surface. Container grown plant materials are known for their high survival rates and low production costs. The containers, usually filled with an admixture of soils and plant nutrients, provide an ideal environment for rapid plant growth. In addition to collecting water and retarding evaporation, the containers shield the plant roots from animal attack, provide some insulation from temperature extremes, and furnish a means for readily moving the plant material from place to place without resort to time consuming and manpower intensive digging or trenching activities.
Despite the best efforts of many nurserymen, contaminated soil mixtures, wind, and animals contribute to the addition of unwanted plants to nursery stock growing containers. Weeds deposited in these containers thrive and, if left unchecked, have a tendency to smother their more valuable neighbors. Weeds not only reduce the amount of sunlight reaching the desired plant materials, slowing their growth rates, but rob the soil of essential nutrients critical to plant development.
Commercial nurserymen have attempted to control the growth of weeds which may develop in containers; however, not with any particular success. Isolation of containers and growing media from weed sources, especially in large scale nursery operations, has been found to be impractical. Physically removing weeds as they sprout is highly labor intensive and inefficient. Therefore, many growers have resorted to the use of costly chemical herbicides for controlling weed growth in their planting containers.
Samples of air, soil, and water taken from locations remote from nurseries which have utilized chemical herbicides over time have included trace amounts of such herbicides. Although the herbicides employed in the United States have been subjected to stringent regulatory testing and approval, the long-term effects on man and the environment are, as yet, unknown. Limiting exposure to such toxic chemicals, however, seems reasonable, and any reduction in the amount of these chemicals leaching from the area of their intended use would undoubtedly be highly beneficial.
Heretofore, the use of mechanical weed barriers, capable of controlling weed growth without large investitures in terms of manpower or chemical herbicides, has been restricted to the use resilient sheets for covering large areas of ground surface. Some of these so-called agrotextile sheets are known to have porous structures permeable to water and air while others are of flexible and impermeable plastic having a closed structure. While the permeable sheets permit water to pass into the ground limiting surface runoff, their interconnected pore spaces are generally so small as to prevent most growing plant shoots from passing therethrough. Furthermore, many agrotextile materials prevent the passage of light thereby inhibiting the growth of plants having the agrotextile placed between such and a light source. The use of such materials in applications involving plant growing containers is believed to be novel and would be greatly beneficial to many nurserymen who would find it desirable to have a device which would control weeds with a minimal use of expensive herbicides, often ineffective for their intended purposes, difficult to apply, and potentially harmful to the environment.